Until recently, base stations deployed in cellular telecommunications systems have consisted of two major components: a large hut and an adjacent tower. The huts have been filled with electronic equipment and a set of radio antennas have been mounted on the tower.
As traffic increases in cellular telecommunications systems, the coverage area for the available channels of a typical base station must decrease in order for the channels to be reused at other base stations. This fact in combination with the progress of miniaturizing electronics will enable future base stations to be configured differently.
Each base station will require significantly less bulky electronics, less power will be required to operate the radios, and the antennas will be mounted on short masts because the radio signals will need to cover less area. As a result, the equipment will be less obtrusive to the environment and installations will require much less real estate and cost less to manufacture. An arrangement in which a pole about twenty (20) feet high with the equipment installed in a small enclosure mounted thereon will replace the hut and tower.
The electronics used in the new type of base stations described above are enclosed in small housings (e.g., 2 feet by 2 feet by 2 feet) and will dissipate on the order of one hundred (100) watts. When the equipment is installed indoors, it is not difficult to cool electronics that dissipate that much power. However, two aspects of outdoor installations create significant difficulties. The first aspect is that such installations must be sealed from the environment to keep out rain and dust. The second aspect is that during the summer season the heat load from the sun adds a burden to the thermal management equipment which can be significantly greater than the load from the electronics. Typically, the way to cool equipment in this situation is to use a fan for circulating air which is mounted adjacent to the electronics within the enclosure.
This way of dissipating heat from the electronics in the enclosure complicates the design of the enclosure because of the need for heat management devices such as heat sinks. As the electronics become more complex, increased heat dissipation is often required, which further increases the size of the enclosure as well as the heat sinks. Thus, heat dissipation capability is a significant design parameter for the enclosure.
The electronics for the base station may be highly reliable, and may require few maintenance calls during the service life of the equipment. Fans, however, are rotating machinery which require regular maintenance or frequent replacement. Service calls for such cooling fans are difficult and expensive because of the specialized equipment (e.g., a "cherry picker" vehicle) required to access the fan mounted at the top of the pole.